1. Field of the Invention
The invention concerns aluminium based alloys of the 7000 series, in the nomenclature of the Aluminium Association (AA), with a high Young's modulus and good mechanical properties of resistance and tenacity; it also concerns a method of obtaining them.
2. Description of the Related Art
Aluminium alloys of the 7000 series, among the most resistant, generally have a Young's modulus E of the order of 70 GPa but not more than 72-73 GPa.
However, the need for light alloys with a higher Young's modulus (F.gtoreq.74 GPa) and high resistance (R.sub.0.2 .gtoreq.530 MPa in the longitudinal direction) is felt in order to lighten structures, particularly in the aeronautical and space fields. These properties must be obtained without markedly prejudicing other use properties such as tenacity (KIC, longitudinal direction .gtoreq.20 MPa .sqroot.m) or resistance to corrosion under tension (non-rupture threshold after 30 days .gtoreq.250 MPa in the short transverse direction and in the test modium in question).
Aluminium based alloys containing Li with a high modulus of elasticity and good mechanical properties are indeed known. However, their working poses complex problems given the reactivity of the Li, and special, expensive working and casting installations are required. The alloys according to the invention can be worked in conventional installations such as are known in the metallurgy of common Al alloys. Moreover the mechanical resistance properties of Al-Li alloys are generally inferior to those of 7000 alloys.
Type 7000 alloys, which are much more charged with alloy elements and obtained by metallurgical treatment of powders, have good mechanical properties and good resistance to corrosion under tension, but a modulus of less than 74 GPa.